Configure user task runner

[csholmq]

Would it be possible to have a user defined task runner as opposed to a workspace tasks.json? Similar to settings.json that sits next to keybindings.json and the snippets folder.

Would allow me to not having to define a default task runner (I run GNU Global gtags for each project) for every single project root I work in.

[BillDenton]

This would be very useful as I use the same tasks for all projects.

[saboco]

Define user templates could be also useful.
http://stackoverflow.com/q/42880813/2776550

[csholmq]

@dbaeumer Possible to move this to a milestone?

[dbaeumer]

The task priority is currently to run task in the terminal and to allow extension to contribute tasks and problem matchers. We will plan more work for tasks when these have been completed.

[dbaeumer]

Dups #1435